The .300 Whisper is a wildcat cartridge developed by J.D. Jones of SSK Industries in 1992, designed to be the most versatile suppressed cartridge possible — capable of firing heavy subsonic bullets (220-240gr) for Hollywood-quiet suppressed shooting, or light supersonic bullets (110-125gr) for conventional hunting applications, all from the same AR-15 platform with a simple barrel swap. The cartridge was later standardized by SAAMI as the .300 AAC Blackout with slightly different dimensions.
Type: Wildcat
Introduced: 1992, United States
Parent case: .221 Remington Fireball
Standardization: None
Bullet diameter: 0.308" (7.82 mm)
Case length: 1.368" (34.75 mm)
Overall length: 2.26" (57.4 mm)
Max pressure: 25,000 PSI
Rim type: Rimless
Primer: Small Rifle
Typical twist rate: 1:8
Muzzle velocity: 1010–2375 fps
Muzzle energy: 498–1379 ft-lbs
Effective range: 250 yd
Common bullet weights: 110, 125, 220, 240 gr
Primary use: suppressor_use, hunting_small_game, military_special_operations
Production status: Obsolete
Also known as: 300 Whisper · .300-221
History: J.D. Jones designed the Whisper concept around the .221 Remington Fireball case, which fits in a standard AR-15 bolt face while providing enough case capacity for heavy .30-caliber subsonic loads. The cartridge gained a following in military special operations communities and among suppressor enthusiasts. Advanced Armament Corporation (AAC) later developed the .300 AAC Blackout as a…
Notable firearms: AR-15 platform, Thompson/Center Contender, Bolt-action customs